Question: Find the slope and y-intercept of the line that is ${\text{perpendicular}}$ to $\enspace {y = -2x + 4}\enspace$ and passes through the point ${(-7, 5)}$. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$
Lines are considered perpendicular if their slopes are negative reciprocals of each other. The slope of the blue line is ${-2}$ , and its negative reciprocal is ${\dfrac{1}{2}}$ Thus, the equation of our perpendicular line will be of the form $\enspace {y = \dfrac{1}{2}x + b}\enspace$ We can plug our point, $(-7, 5)$ , into this equation to solve for ${b}$ , the y-intercept. $5 = {\dfrac{1}{2}}(-7) + {b}$ $5 = -\dfrac{7}{2} + {b}$ $5 + \dfrac{7}{2} = {b} = \dfrac{17}{2}$ The equation of the perpendicular line is $\enspace {y = \dfrac{1}{2}x + \dfrac{17}{2}}\enspace$. ${m = \dfrac{1}{2}, \enspace b = \dfrac{17}{2}}$